Binocular viewing devices such as, for example, those mounted on microscopes usually comprise two rhomboid-shaped prisms reflecting two beams spaced apart by the interpupillary distance and observed by the oculars. These devices are very suitable when one wishes to observe an aerial image which is formed in the lenses of rhomboid-shaped prisms. These devices are not satisfactory when one wishes to observe a real image with a short ocular focal length.
Optical apparatus for binocular viewing comprising only a single optical system providing two beams at the interpupillary distance which may be observed directly are also known. These binocular apparatus are limited because they do not allow short focal lengths without viewing becoming difficult. Moreover, the correction of aberrations is difficult.
In nocturnal observation instruments fitted with light intensification tubes such as those described for example in French Pat. No. 2,123,564 and its additions, it is necessary to observe the real image at the exit to the light intensification tube. Known binocular devices are used with difficulty to observe this image especially if one wishes the focal length of the eyepieces to be as short as possible.